Effect of BaSnO 3 on the microwave dielectric properties of Ba 2 Ti 9 O 20
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Effect of BaSnO3 on the microwave dielectric properties of Ba2 Ti9 O20 Ki Hyun Yoon, Jae Beom Kim, and Woo Sup Kim Department of Ceramic Engineering, Yonsei University, Seoul, 120-749, Korea
Eung Soo Kim Department of Material Engineering, Kyonggi University, Suwon, Korea (Received 21 August 1995; accepted 12 April 1996)
The effect of BaSnO3 on the phase formation and the dielectric properties of Ba2 Ti9 O20 was investigated as a function of the amount of BaSnO3 in the temperature range of 20 ±C to 80 ±C at 7 GHz. In the reaction of 2BaCO3 1 9TiO2 ! Ba2 Ti9 O20 1 2CO2 ", the batch with the addition of BaSnO3 enhanced the reactivity compared to the batch with the addition of SnO2 . The enhancement of reactivity caused single phase Ba2 Ti9 O20 to form effectively with less amounts of BaSnO3 . As the amount of BaSnO3 increased up to 0.03 mol, the unloaded Q increased due to an increase of the Ba2 Ti9 O20 phase; for further addition of BaSnO3 over 0.3 mol, the unloaded Q decreased due to the increase of rutile and BaTi4 O9 phases. The dielectric constant increased with increasing BaSnO3 . As single phase Ba2 Ti9 O20 was present in the specimen, the Q ? f0 value, the dielectric constant, and the TCF were approximately 37,900, 38.7, and 1.7 ppmy±C, respectively.
I. INTRODUCTION
Microwave dielectric resonators used in long-range communications need a high dielectric constant K to minimize size [D (diameter) / 1yK 1/2 in TE011 mode], a high Q factor for high frequency selectivity, and a low temperature coefficient of resonant frequency for frequency stability.1 Since the first use of TiO2 as a microwave dielectric resonator, various other materials have been investigated,2,3 including Ba2 Ti9 O20 , (ZrSn)TiO4 , Ba(Mg1/3 Ta2/3 )O3 , and BaO–PbO –Nd2 O3 –TiO2 . Monophase Ba2 Ti9 O20 , first synthesized by Jonker and Kwestroo,4 has been shown to have the dielectric properties of K 39.8, Q ? f0 8000, and TCK 2 ppmy±C (TCF 224 ppmy±C) at 4 GHz.1,4 Amin et al.5 reported that the evolution of CO2 in the reaction of BaCO3 and anatase TiO2 happened at a lower temperature than that in the reaction of BaCO3 and rutile TiO2 even though the reaction rate was identical, which was due to crystalline form change in the anatase-rutile transition. O’Bryan and Thomson6 reported that some Ba2 Ti9 O20 needs to be created within the mixed oxide powders after calcination as a prerequisite for the complete transformation of the mixed powders of raw materials into monophase Ba2 Ti9 O20 during sintering. Jaakola et al.7 noted that a reaction temperature of 1150 ±C or higher is necessary for the crystallization of Ba2 Ti9 O20 phase within a reasonable time span in a mixture of BaCO3 –TiO2 . Furthermore, later studies8 revealed a curvature of the Ba2 Ti9 O20 equilibrium phase boundary in the system BaO–TiO2 at 1996
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 8, Aug 1996
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high temperature, which is an additional complication in forming monophase Ba2 Ti9
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